Progress in pathology A review of adenoid cystic carcinoma of the breast with emphasis on its molecular and genetic characteristics ☆ Semir Vranic MD a , Richard Bender MD b , Juan Palazzo MD c , Zoran Gatalica MD, DSc b, ⁎ a Department of Pathology, Clinical Center of the University of Sarajevo, Sarajevo, Bosnia-Herzegovina 71000 b Caris Life Sciences, Phoenix, AZ 85040 c Department of Pathology, Anatomy, and Cell Biology, Jefferson Medical College, Philadelphia, PA 19107, USA Received 23 November 2011; revised 4 January 2012; accepted 6 January 2012 Keywords: Breast cancer; Triple-negative breast carcinoma; Special types; Adenoid cystic carcinoma Summary Breast carcinomas that do not express estrogen receptor α, progesterone receptor, or human epidermal growth factor receptor 2 are frequently grouped together as “triple negative” and considered an aggressive type of breast malignancy; however, this group is not homogeneous. Adenoid cystic carcinoma of the breast is a rare type of breast cancer with such triple-negative features and, generally, a more favorable clinical course. This comprehensive review describes diagnostic, molecular, and clinical features of adenoid cystic carcinoma and compares them with those of triple-negative breast carcinomas of no special type. © 2013 Elsevier Inc. All rights reserved. 1. Introduction Invasive breast carcinoma includes a heterogeneous group of tumors with diverse morphologic, molecular, and clinical features [1,2]. Morphologically, invasive ductal carcinoma of no special type (NST) is the most common histologic type, constituting up to 75% of all breast carcinomas [1,3]. The remaining 25% represent various special types with at least 18 different histomorphologic entities including adenoid cystic carcinoma (ACC), a salivary gland–type of breast carcinoma. Recent molecular and gene expression profiling studies have defined a smaller number of breast carcinoma sub- groups including a relatively large basal-like subgroup that overexpresses basal cell markers [4-6]. Using this molecular classification, basal-like tumors represent the most common (50%-85%) and distinct group of triple-negative breast carcinomas (TNBCs; with basal-like features). Besides the lack of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (Her-2/neu) [2,7-12], they, in addition, express 1 or more basal cell markers (eg, cytokeratins 5, 5/6, 14, and 17). TNBC with basal-like features is also not uniform and includes several histologic subtypes such as ACC of the breast. This review will focus on ACC of the breast and compare it with the other TNBCs with basal-like features. 2. Special types of breast carcinoma Special types of breast carcinoma are a heterogeneous group with various morphologic, immunohistochemical, and molecular characteristics [13]. These include a group of salivary gland–type tumors (benign and malignant) such as ☆ Conflict of interest: We declare that we have no conflict of interest. ⁎ Corresponding author. E-mail address: zgatalica@carisls.com (Z. Gatalica). www.elsevier.com/locate/humpath 0046-8177/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.humpath.2012.01.002 Human Pathology (2013) 44, 301–309